1. Field of the Invention
The present invention relates to a machine tool equipped with a pallet changer for automatically replacing a preceding-process pallet with a next-process pallet. The invention also relates to the pallet changer.
2. Discussion of the Related Art
Machine tools such as vertical machining centers are generally equipped with a pallet changer. Upon completion of the machining operation of a workpiece on a preceding-process pallet placed on a machining table, the machine tool automatically changes the preceding-process pallet with a next-process pallet on which an unmachined workpiece is held and which has been stationed in a setup position.
Conventional pallet changers of this kind include, for example, those of the pivot type where a pivot arm is provided between a machine-side changing position and a setup position. Additionally, the advancing-and-retreating pivot type where a pivot arm is advanced and retreated and further pivoted have been provided. These pallet changers are disposed close to the machine tool.
The pivot-type pallet changers described above have to be located close to the machine tool for structural reasons. This results in a problem because the pallet changer obstructs the maintenance work of the machine tool operator thereby making it difficult to ensure the proper working space.
For the type of pallet changer where the pivot arm is advanced and retreated, the working space cannot be ensured by making the pallet changer retreatable to a position away from the machine tool. If one tries to make the pallet changer retreatable to a position located away from the machine tool, the pallet changer becomes complex in structure and moreover, in some cases, this structure could not be adopted due to the structure of the replacement position of the machine tool.
An object of the invention is to provide a machine tool, as well as a pallet changer therefor, which allows a working space around the machine tool to be ensured without causing any complications in the structure and which is also applicable to a wide range of applications.
In order to achieve the above and other objects of the invention, according to a first aspect of the invention there is provided a machine tool which comprises a pallet changer at a front of a machine body for automatically changing a preceding-process pallet loaded with a machined workpiece thereon with a next-process pallet loaded with an unmachined workpiece thereon, wherein a working space is provided between the machine body and the pallet changer.
In a second aspect of the invention, there is provided a pallet changer for use in a machine tool to automatically change a preceding-process pallet disposed in a machine-side changing position and loaded with a machined workpiece thereon with a next-process pallet disposed in a setup position and loaded with an unmachined workpiece thereon, said pallet changer comprising: a relay changer mechanism for advancing and retreating at least one of the preceding-process pallet and the next-process pallet between the machine-side changing position and a relay changing position; and a pivotal changer mechanism for changing the preceding-process pallet with the next-process pallet by a pivoting operation in a position between the relay changing position and the setup position.
In a third aspect of the invention, there is provided a pallet changer for use in a machine tool as described in the second aspect, wherein the relay changer mechanism advances and retreats the preceding-process pallet and the next-process pallet through up-and-down and advance-and-retreat linear motions for lifting the preceding-process pallet disposed in the machine-side changing position and the next-process pallet disposed in the relay changing position, thereafter linearly conveying the preceding-process pallet to a site upward of the relay changing position and the next-process pallet to a site upward of the machine-side changing position, and further lowering the preceding-process pallet to the relay changing position and the next-process pallet to the machine-side changing position.
In a fourth aspect of the invention, there is provided a pallet changer for use in a machine tool as described in the fourth aspect, wherein the relay changer mechanism comprises a first arm member mounted on a frame member so as to be advanceable and retreatable, and a second arm member supported on the first arm member so as to be advanceable and retreatable relative to the first arm member, and a speed-increasing mechanism is further provided between the first arm member and the second arm member for advancing and retreating the second arm member by making use of the advance-and-retreat motions of the first arm member.
In a fifth aspect of the invention, there is provided a pallet changer for use in a machine tool as described in the fourth aspect, wherein the speed-increasing mechanism is structured so that the first arm member is equipped with a driving-side chain mechanism and a driven-side chain mechanism, each having an endless chain on a pair of sprockets disposed so as to be spaced from each other in an advance-and-retreat direction, one-end side sprockets of the two chain mechanisms being coaxially and co-rotationally connected to each other, the chain of the driving-side chain mechanism being fixed to the frame member and the chain of the driven-side chain mechanism being connected to the second arm member.
According to the first aspect of the invention, since the working space is provided between the machine body and the pallet changer, the operator is allowed to perform tool maintenance as well as other work on the machine body side while being positioned in the working space. Thus, the workability of the machine tool can be improved.
According to the second aspect of the invention, since the relay changer mechanism for advancing and retreating the preceding-process pallet and the next-process pallet between the machine-side changing position and the relay changing position is provided, the pivotal changer mechanism can be placed away from the machine tool without complicating the structure of the pivotal changer mechanism. This allows the working space to be ensured between the machine tool and the pallet changer and thus the workability of the machine tool can be improved.
Further, since the relay changer mechanism advances and retreats to advance and retreat the pallet placed at the machine-side changing position or the pallet placed at the relay changing position, the relay changer mechanism is structurally adaptable to the changing positions of the machine tool. This allows the range of applications to be widened.
According to the third aspect of the invention, since the relay changer mechanism advances and retreats the preceding-process pallet and the next-process pallet through up-and-down and advance-and-retreat linear motions for lifting the preceding-process pallet placed at the machine-side changing position and the next-process pallet is placed at the relay changing position, it linearly conveys the preceding-process pallet to a site upward of the relay changing position and it conveys the next-process pallet to a site upward of the machine-side changing position. Also it further lowers the preceding-process pallet to the relay changing position and the next-process pallet to the machine-side changing position. As a result of this, it becomes possible to propose a concrete structure that allows the pallets to be advanced and retreated or seated along with each other as described in the first aspect.
According to the fourth aspect of the invention the relay changer mechanism is equipped with a speed-increasing mechanism between a first arm member and a second arm member supported on the first arm member. The relay changer mechanism serves to advance and retreat the second arm member by making use of advance-and-retreat motions of the first arm member. As a result of this, the second arm member can be advanced and retreated to a greater extent only by driving the first arm member. This allows the working space to be ensured more securely while any complication in the structure can be suppressed.
According to the fifth aspect of the invention, the speed-increasing mechanism is so constructed that the first arm member is equipped with a driving-side chain mechanism and a driven-side chain mechanism. Also one-end side sprockets of the two chain mechanisms are coaxially and co-rotationally connected to each other. The chain of the driving-side chain mechanism is fixed to the frame member and the chain of the driven-side chain mechanism is connected to the second arm member. As a result of this arrangement, it becomes possible to achieve a structure that allows the speed-increasing mechanism to advance and retreat the second arm member to a greater extent only by driving the first arm member to advance and retreat.